Myocardial infarction is irreversible necrosis of heart muscle cells caused by ischemic heart disease, which is characterized by coronary blood flow diminished to the level unsustainable to the metabolic demand of myocardium.
Common symptoms of ischemic heart disease include angina, shortness of breath, or fatigue. Often angina is worsened if the patient exerts after a meal, or walks into a cold weather, or suffers from emotional stress.
The major pathogenesis of myocardial infarction is coronary artery stenosis, leading to myocardial cells starved for oxygen (hypoxia) and glucose, the result of which is death or permanent damage of myocardial cells (myocytes).
The etiologies for coronary artery stenosis are fixed atherosclerotic obstruction, acute plaque rupture, coronary artery thrombosis, and vasospasm. In order to study myocardial infarction, lab models are established by occlusive ligature of coronary artery of experimental animals to reproduce ischemia caused by coronary artery stenosis, or by deprivation oxygen (hypoxia) and glucose supply to cultured myocardial cells.
Morphologically the area of necrotic myocardium corresponds to the area where occluded coronary artery supplies. The myocardial tissue affected turns from pallor to cyanotic, further to softened yellow central area with a hyperemic rim. Eventually the dead myocardial tissue is replaced by a fibrotic white thin scar. The severity of the damage to myocardium is proportional to the area affected by coronary artery stenosis and the time duration of ischemia.
Under microscope the ischemic myocardial cells display various morphological changes ranging from myocytolysis, eosinophilic cell infiltration with intercellular edema of the myocardium, acute inflammation of the myocytes, macrophages removing dead myocytes, granulation tissue, to scar tissue.
Biochemical lab diagnosis provides specific, sensitive and timely results indicating myocardial cell stress, injury, and death. The lab test markers relevant to myocardial muscle cell's current biomedical conditions are creatine kinase sub-fraction MB (CK-MB) level, cardiac troponin levels (troponin-T and troponin-I), Lactate Dehydrogenase (LDH) level and myoglobin level.
Elevation of CK-MB indicates acute myocardial cell injury, since it is a specific enzyme in myocardial cells and a good marker of injury of myocardial cells. Isoforms 1 and 2 of CK-MB can also be tested, and the ratio of the two CK-MB isoforms can provide further information about the injury condition of myocardial cell.
Troponin-T and Troponin-I are proteins in myocardial cells. Elevation of the Troponin-T and Troponin-I indicate that myocardial cells are injured.
Elevation of LDH level is another indicator of myocardial infarction.
Myoglobin is structure protein of myocytes. Increase of its level indicates myocardial infarction.
Numerous drug treatments to combat coronary heart disease have been developed. Commonly prescribed drugs to treat coronary diseases are beta-blockers, nitrates, calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, and antiplatelet coaggregation drugs.
Beta-blockers are prescribed to alleviate the effect of adrenaline and noradrenaline on the heart. Nitroglycerin dilates coronary blood vessels instantly. Calcium channel blockers prevent blood vessels from constricting and counter coronary artery spasm. ACE inhibitors, such as ramipril reduce the risk of heart attack. Antiplatelet coaggregation drugs, such as aspirin reduce the aggregation of platelets so that they do not clump and stick on blood vessel walls. Some of the drugs are used in combination to prevent or reduce ischemia and to minimize symptoms.
Searching for new drugs to treat coronary heart disease has been an on going effort worldwide. Natural resources have been the dependable sources for new drug development for long time. New drugs developed from substances originated from plants are believed less dependent forming, with fewer side effects.